Digital cameras and other image capture devices have pixel based sensors. In the case of a digital camera the sensor is part of the digital camera back, hereinafter referred to simply as the back. The sensor comes in two types, those that substantially cover the full image capture so that only a single image capture operation is needed per image, and those in which the image size is a fraction of the full image capture area, so that the sensor needs to be shifted for separate captures over the capture area. The former are referred to herein as large area sensors. In state-of-the-art digital cameras or cameras with digital camera backs having large area sensors, the most costly component is usually the image sensor. This is primarily because fabrication yield, that is the proportion of sensors manufactured that are passed for use, is approximately proportional to the area. Typically, for sensors larger than 16 mm×24 mm, less than half of the sensors manufactured are passed as suitable for imaging. Sensors that are considered as not being suitable for imaging are generally rejected because they have blemishes that cannot be corrected using conventional means. Blemishes are regions of one or more unreliable pixels. In general single pixel, or close to single pixel, blemishes can be compensated for using conventional means. However, certain larger types of blemish such as clusters of more than 2×2 unreliable pixels, or adjacent multi-row or multi-column blemishes cannot be compensated for using conventional means and sensors having such blemishes are typically rejected.
An example of conventional blemish compensation is disclosed in JP3296375A2, which discloses a blemish correcting circuit for implementing blemish correction processing by subtracting a signal at a level indicating blemish level data from an output signal of a pixel. U.S. Pat. No. 5,159,457 assigned to Sony Corporation, discloses an adjustment operational mode, in which a charge coupled device (CCD) having pixels with a temperature dependent blemish is driven so that the CCD accumulates N times as much charge as in an ordinary operational mode. A corresponding offset voltage is supplied to a temperature sensor so that a blemish compensation signal from a blemish compensation signal generator can be adjusted with high accuracy. In the adjustment mode, the temperature of the CCD is raised, so that the level of the blemish component of the signal output from the CCD is large enough to be accurately adjusted. In an ordinary operational mode, the compensation signal from the blemish compensation signal generator which has been level-adjusted with high accuracy in the adjustment operational mode is added to an image pick-up output signal of the CCD to produce a blemish compensated signal adjusted with high accuracy. The above system is not suitable for most types of manufacturing blemish however.
Certain backs are designed to capture a full image in 3 separate image capture operations or shots. An example is the Leaf Volare camera back which implements color image capture by taking each shot through a different colored filter. Another example of multiple shot image capture is that of the Leaf Cantare XY camera back and similar devices, which use a color filter array sensor. The back is designed to capture the image in two or three shots wherein the sensor is moved by an exact pixel shift between the shots in order to obtain full color sampling. Such camera backs generally use a small size sensor, which does not cover the full imaging area, since the smaller sensor gives a higher fabrication yield and it thus cheaper to produce. Large area sensor, which cover the imaging area are prohibitively costly.
It would be advantageous to provide a camera back with a sensor whose area size is closer to the optical imaging area size, at a reduced cost.